Considerable effort is being expended to develop wings capable of generating tractive force for the purposes of powering a user on a variety of vehicles that are tethered solely by flexible lines. Such wings can generally be considered kites. The development of kites capable of generating significant force has made possible numerous recreational pursuits. For example, kite surfing or kite boarding refers to a sport involving the use of a wind powered wing to pull the participant on a vehicle across a body of water. Similar sports involving the use of appropriately configured vehicles to traverse sand, earth, snow and ice are also being pursued. One of skill in the art will also recognize that wind powered wings can be used in any number of other applications, whether recreational or practical. With the development of these applications has come an increasing demand for kites having improved characteristics.
One type of kite that has achieved popularity is a leading edge inflatable (“LEI”) kite, typically comprising a semi-rigid framework of inflatable struts or spars that support a canopy to form the profile of the wing. This basic design is taught by U.S. Pat. No. 4,708,078 to Legaignoux, et al. The development of the LEI kite is generally credited with spurring the development of modern kite surfing due to its ability to be relaunched from the water's surface.
Despite the popularity of LEI kite designs, they do suffer from certain, inherent challenges. The most successful LEI kites currently employ a four-line control system, in which two steering lines are secured to the trailing edge and two front lines are secured to the leading edge. Altering the relative length between the steering lines and the front lines adjusts angle of attack, or the trim, of the kite.
As can be appreciated, the degree of control an operator has over the aerodynamic characteristics of the kite can help optimize its usefulness. For example, aerodynamic efficiency, relaunchability, performance, safety, handling and power management are all interrelated aspects of the kite's design and the control system used to fly the kite. In one instance, attempts to improve the performance of a kite often involve increasing the aspect ratio of the wing. However, the ability of the kite to be relaunched tends to be inversely related to the aspect ratio. Likewise, one aspect of a kite's efficiency is its lift to drag ratio, but increasing this ratio can have adverse effects on the handling of the kite. Yet another example is the balance between trim control and steering. By positioning the attachment of the front line closer to the steering line on the wingtip, a greater range of attitude can be effected given the same relative change in length between the steering line and the front line. However, the turning speed of the kite is improved by increasing the width of the wingtip, which tends to increase distance between the front line attachment and steering line attachment.
Thus, conventional kite design often involves balancing between two or more competing attributes, wherein the entire system is subject to the constraints of the amount of control available.
The issue of safety, as referenced above, is also an important factor in the design of a LEI kite system. Power kites are capable of generating large forces that contribute to the enjoyment of the sport. However, these same forces can also pose significant safety hazards to the user and to bystanders when inadequate control is provided. This can occur if the wind strength increases beyond an acceptable amount, if the user does not or cannot utilize the control system appropriately or if the control system becomes compromised, such as by twisting, tangling or breaking the lines. Therefore, most kite designs and control systems offer a means for substantially reducing the amount of power exerted by the kite. Conventional systems include methods of restraining one of either the front lines or the steering lines while allowing a significant amount of slack in the remaining lines. Ideally, this has the effect of corrupting the aerodynamic profile of the kite so that essentially all the lifting forces are extinguished. However, the conventional systems suffer from a number of drawbacks, including the possibility that the kite will not adequately depower, the significant chance that the lines will become tangled and the difficulty in relaunching the kite after it has been depowered.
One prior art technique for improving safety is the inclusion of another control line, a fifth line that is secured to the leading edge. These systems recognize the ability to effectively depower the kite by tensioning the fifth line while slackening the remaining four lines. Some of these systems also recognize that the fifth line can also impart some structural stability to the kite by restraining the leading edge. Indeed, certain fifth line systems employ a bridle arrangement to help lock the curvature of the leading edge. Thus, conventional fifth line systems do offer a complete depower function and the potential for increased stability. However, such systems do not provide a means for selectively controlling the aerodynamic profile of the kite during flight to improve the handling characteristics. The prior art systems also fail to offer a method for dynamically varying and fixing tension on the fifth line to trim the kite while flying.
Accordingly, it is an object of the present invention to provide a control system for a LEI kite design that offers improved aerodynamic control.
It is also an object of the present invention to provide a control system for a LEI kite design that offers enhanced adjustment of the kite's angle of attack as compared to conventional four-line control systems.
It is another object of the present invention to provide a control system for a LEI kite design that provides modification of the kite's projected area.
It is yet another object of the present invention to provide a control system for a LEI kite design that allows a user to completely depower the kite without tethering to the steering lines or the front lines.
It is an also an object of the present invention to provide a method for controlling a LEI kite that offers improved adjustment of the kite's performance characteristics.